1. Technical Field
The present invention relates to an optical pulse amplifier and, more particularly, to an optical pulse amplifier using a chirped grating.
2. Related Art
An erbium doped fiber amplifier has saturation energy of about 1 .mu.J, at which the power of an output signal does not increase, even if the power of an input signal is increased. Peak power of an ultrashort pulse amplified at this energy is very high, (e.g., 1 MW at 1 pico second pulse), so that the intensity thereof greatly increases if the energy is confined to the core of an optical fiber, thereby causing non-linear effects and distorting the pulse. Also, a spectral hole burning effect occurs, in which amplification is not achieved due to a decrease in the stimulated emission gain.
To solve these problems, the ultrashort pulse is stretched, using a bulk diffraction-grating stretcher to lower the peak value of the power within the amplifier.
However, a problem wit the method using a bulk diffraction-grating stretcher is that the diffraction-grating arrangement is sensitive to polarization and is not strong. Also, the method causes much diffraction loss and distorts the profile of an output beam.